Free and opposed piston motor compressor unit



R. PATERAS PESCARA Aug. 31', 1931.

FREE AND OPPOSED PISTON MOTOR COMPRESSOR UNIT 2 Sheets-Sheet 1 mam,-

116d July 11, 1936 .ziziiii fiat/l i i/BM: Jaac are,

Patented Aug. 31,1937

DEED STATES- FREE AND OPPOSED PISTON MOTOR COM- PRESSOR T Raul Pateras Pescara, Paris, France Application July 11, 1936, Serial No. 90,235 In BelgiumJuly 13, 1935 10 Claims. (Cl. 230-56) This invention relates to internal-combustion motor-compressor units 01' the free and opposed piston type, and more particularly to such units comprising at least two compression stages; and

it relates still more particularly to multi-stage free piston motor compressors of the asymmetrical type, as hereinafter defined.

In my co-pending application Ser. Number 650,351, I disclosed certain improvements in internal-combustion free and opposed piston motor compressor units of the symmetrical type, meaning thereby such units comprising one or more pressure stages, each of which stages comprises two identical compressor cylinders symmetrically disposed at opposite ends of a common mo tor cylinder. Said improvements related mainly to the provision of pneumatic means adapted to supply the energy required to return the freely-reciprocating pistons, at the end of each 20 Working stroke, to their correct respective positions at the beginning of the next working stroke, regardless of the variations in the length of said working strokes. They consisted, namely, in providing three combined sources of energy for the return stroke: First, the expansive energy of the residual compressed gas remaining in the clearance space of the compressor cylinders, which energy supply is a negative linear function of the length of stroke; secondly, the 39 energy supplied to the high-pressure pistons by the compressed gas delivered by the low-pressure stage to the high-pressure stage; and thirdly, the energy avaiiable from auxiliary pneumatic cushioning spaces permanently supplied with high- 35 pressure compressed gas by the high-pressure stage; both the second and third energy supplies being positive linear functions of the length of stroke, and hence adapted to balance at all times the energy available from said first source,

and so to render the total supply '01 return energy substantially constant, regardless of the variations in the length ofV-the working strokes.

The main p rpose of the present invention is to extend the application of the improvements 5 disclosed in the above-mentioned co-p'ending apv plication to multi-stage free and opposed piston motor compressors of the asymmetrical type- "meaning thereby such units comprising at least two compression stages, each of which stages comprises only one compressor cylinder, instead of two, as in the symmetrical type, the cylinders of successive compression stages being suitably disposed at opposite ends of the motor cylinderfor example, in a two-stage compressor unit, the low-pressure stage being at one end of said mo- 5 tor cylinder, and the'hig'h-pressure stage at the other end.

The principal object of my invention is to provide a, multi-stage motor-compressorunit of the,

asymmetrical type, as hereinbefore defined, comprising combined pneumatic means adapted to supply energy for the return stroke of the mo-- tive pistons, and to substantially equalize the aggregate forces acting on the oppositely-reciprocating piston groups. 7

Another object is to provide a multi-stage mo tor-compressor unit as above, in which said comhined penumatic energy supplying means com prise. Firstly, a pneumatic cushion remaining in the clearance space'of the low-pressure cylin- 2o der; secondly, the volume of partly-compressed gas deiivered by each pressure stage to the next higher pressure stage-for exampie,"in a twostage compressor unit, by the low-pressure to the highspressure stage which partly-compressed gas assists materially in the return of the piston; and thirdly, auxiliary pneumatic compensating means adapted to simultaneouslysupply the balance required for the return stroke of the mo tive pistonsand to equalize the aggregate forces acting on the oppositely-reciprocating piston groups, with a view to relieving the synchronizing linkages interconnecting'said oppositely-reciprocating piston groups from anystraius other than those due to their owninertia,

A. further object is to provide a two-stage motor-compressorunit of the asymmetrical type. in which said auxiliary pne lmaticycompensating means consist of a single gas cushioning cylinder acting onthe low-pressure compressor piston. 40

A still further object is toprovide-a two-stage motor-compressor unit of the type;,'described, in which the combined pneumatic energy supplying means, as hereinbefore described, to provide an amount of energy'for the' stroke which is substantially constantgregfidless of the variations in the length of the-working stroke. and to further equalize, at least atbne point of the working stroke, the aggregate forces acting on the oppositely reciprocating A still further object is to provide a two-stage motor-compressor unit of the type described, in which said combined pneumatic energy supplying means co-act to provide of energy for the re- 5 turn stroke which is variable, for varying lengths of the working stroke, within given predetermined lower and upper limits, and to further equalize, at least at one point of the working stroke, the forces acting on the reciprocating parts.

A still further object is to provide a two-stage motor-compressor of the type described, in which the action of the above mentioned combined pneumatic means is adjusted by subjecting the rear or inactive faces of the low and high-pressure compressor, pistons to gas pressures other than atmospheric.

A still further object is to provide a two-stage motor-compressor unit of the type described, in

which the space between the two compressor pistons is inclosed within a casing, and all or part of said space is used to compress or store gas for motor scavenging purposes.

Other objects and advantages of my invention will appear to one skilled in the art, from the following description, with reference to the accompanying drawings, it being understood of course, that said description and drawings are' given by way of illustration, only, and should not be construed as limiting the scope of my, invention.

In these drawings: Fig. 1 shows diagrammatically, in longitudinal cross-section, a two-stage motor-compressor unit embodying my invention;

, Fig. 2 shows a diagram of the forces acting on the low-pressure compressor piston at all points of the working and return strokes;

Fig. 3 shows a similar diagram for the highpressure compressor piston;

Fig. 4 a similar diagram for the auxiliary compensating cylinder.

Fig. 5 is a view similar to Fig. 1 of a modification of the invention. 5 In one of the preferred embodiments of my invention, I provide a motor cylinder l co-acting with two axially slidable motive-pistons 21 and 22 adapted to reciprocate in opposite directions within said cylinder; and I further provide lowpressure and high pressure compressor pistons 31 and 32, the first rigidly connected to motive piston 21 and the second to motive piston 22, said compressor" pistons co-acting respectively with low-pressure and high-pressure cylinders 41 5 and 42. -In order. to equalize the forces acting respectively on the oppositely reciprocating assemblies comprising respectively motive and compressor pistons 21 and 31 and 22 and 3:, and to supply the balance of energy necessary for the return go of thepistons, I provide'an auxiliary compensating pneumatic cylinder 6 with co-acting piston 5 rigidly connected to compressor piston 4 and connect said compensating cylinder 6 to the delivery of the high-pressure compressor cylinder. This 5 is,equivalent to applying to a fraction of the area of the low-pressure compressor piston a constant compensating super-pressure equal to the daily! ery pressure of the'high-pressui'e stage.

In order to fulfill the difi'erent known require-' 7 ments insuring maximum operating efliciency in multistage compressors, the following dimensional relations must be observed:

Assuming S1 and S: to be respectively the surface areas of the low-pressure and high-pressure 7 compressor pistons 31 and 31, and p1 and p: to

be respectively the delivery pressures of the lowpressure and high-pressure stages, and m the initial suction pressure, which is usually that of the atmosphere, it may readily be seen that, in two pressure stages in which the corresponding phases occur simultaneously, the following known relation must obtain:

In order that the areas of the force-stroke diagrams of the low-pressure and high-pressure stages be equal, a second relation, also well known, must obtain:

These two relations insure the maximum efiiciency in a two-stage compressonand under these conditions, the low-pressure and high-pressure compressor pistons 31 and 3: are subjected on their working faces to equal and opposite total forces. Any unbalance in the aggregate forces acting on the opposed reciprocating, groups of parts will therefore necessarily result from the fact that the rear, or inactive faces of compressor pistons 31 and 32 are subjected to unequal forces, which is the case when said inactive faces are subjected to the same pressure, such, for example, as that of the atmosphere.

According to one embodiment of the invention, the auxiliary compensating cylinder 6 is adapted to compensate said unbalanced forces. In the case most commonly found in practice, where the inactive faces of compressor pistons 31 and 32 are subjected to atmospheric pressure, it may be shown that said unbalanced forces are accurately compensated when the area Sc of the auxiliary compensating piston 5 satisfies the following relation:

When the three relations mentioned above are satisfied, even through the motor-compressor unit is asymmetrical, the opposed reciprocating piston groups are subjected to equal and opposite forces at all points of the working cycle, and the synchronizing means interconnecting said reciprocating parts, such, for example, as connecting rods |21 and I22 and cranks l3, never have to transmit energy from one group to the other, which is the condition obtaining in symmetrical units.

Fig. 2 indicates the diagram a1 b1 01 d1 of the total force S1 37 acting on the working face of the low-pressure compressor-piston 31; whereas line f1 d1 indicates the constant force exerted on the inactive face of said piston. Fig. 3 shows the diagram a: b: 02 d2 of the total force S2 12 exerted on the working face of the high-pressure compressor piston 32, whereas line f2 92 shows the constant force acting on the-rear or inactive face of said piston 31, which constant force is'different from that acting' on piston 31. The areas indicated in oblique cross-hatching in Figs. 2 and 3' represent the energy available for the return of the pistons. Fig. 4 shows a diagram f1 d1 ga which represents the difference between the areas I: gz d: a: be and ii 0.1 in, which difference must be added to f1 01 in in order to equalize at all points of :the cycle the aggregate forces acting upon the reciprocating parts.

I attain this result:

By designing the compensating cylinder 6 so as to adapt it to compensate the unbalanced pressor cylinder, a volume of partly compressed forces acting on the reciprocating parts, so that the energy available from the first and second sources mentioned hereabove for the return of the pistons always be sumcient to give the reouired final compression pressure in the combustion chamber, regardless of the length of the.

working stroke;

Preferably the compensating cylinder 5 is de signed so as to adapt it to supply the energy rere quired for the return stroke. while the equalizing of the-iorces acting in the opposed reciprocating assemblies is accomplished by applying to the inactive faces of the compressor pistons 31 and in suitable pressures, which may be above or be low atmospheric pressure.

Motor-compressor units or the type in question operate on the two stroke cycle, and must therefore be provided with scavenging means. Said means may be provided by inclosing the space 9 between the low-pressure and high-pressure pistons 31 and 32 within a closed casing. It is evident that the alternating'motion of said pistons periodically increases and reduces the volume of said inclosed space, which when provided with 5 suction and dischargemeans, such as inlet valves iii, inlet ports ii in the combustion chamber, and combustion outlet or exhaust iii is adapted to act as a scavenging compressor. In this case, pistons 31 and 32 being both subjected to the scavenging pressure, said pressure has no tendency to upset the balance of forces.

It is also possible as shown in Fig. 5 to use as a scavenging pump a chamber ill obtained by providing a gas-tight partition l 6 closing the rear end or the low-pressure cylinder ll, thus making the low-pressure stage double-acting. -Chamher it communicates with the atmosphere by valves i9 and with the other portion of easing 9 by valves all. Under these conditions, the scav- 4o enging compressor would tend to unbalance the reciprocating parts; but this efiect may be rendered negligible by subjecting the rear face of the I high-pressure-piston 32 to the delivery pressure of the scavenging unit; for example, by using the space 9, inclos'ed in the closed casing, as a. scavenging air storage reservoir,

It should he understood that I do not wish to be limited to the structural details described and illustrated, for. obvious modifications thereto will I occur to persons skilled in the art.

What I claim is:

l. A two-stage internal-combustion free and opposed piston motor compressor unit, comprising a motor cylinder, two axially movable motive pistons in said cylinder, a combustion chamber between said motive pistons, a low-pressure compressor cylinder at one endof said motor cylinder, a high-pressure, compressor cylinder at the other end oi said motor cylinder, compressor pistons axially slidable within said low and high pressure compressor cylinders, rigid operative connections between one oi said motive pistons and said low-pressure compressor piston, and between the other motive piston and said highpressure compressor piston, conduit means interconnecting'said low and high pressure compressor cylinders, and pneumatic means adapted to supply an amount'of energy for the return stroke which is substantially independent of the length the aggregate forces acting on the oppositely reciprocating piston groups atleast at one point of the working cycle, said pneumatic means comprising, in combination, a gas cushion inclosed 75 in the clearance space of the low-pressure comof the working stroke and to equalize substantially 1 gas delivered by said low-pressure cylinder to said high-pressure cylinder, and an auxiliary compensating cylinder adjacent to, and in alignment with, said low-pressure compressor cylinder, an axially slidable compensating piston within said auxiliary cylinder, a rigid operating connection between said compensating piston and said low-pressure compressor piston, and means forintroducing gas into said auxiliary compensating cylinder at the pressure of delivery from the high-pressure stage.

2. A two-stage motor-compressor unit apcording to claim 1, in which said means for introducing gas into said auxiliary compensating cylinders comprises a pipe permanently connecting said cylinder with thegas delivery from the highpressure compressor cylinder.

3. A two-stage motor-compressor unit according to claim 1, in which the diameters of the motive pistons, oi the high and low-pressure compressor pistons and of the auxiliary compensatmg piston, are so interrelated as to provide simultaneously an amount or energy for the return stroke which is substantially independent of the length of the working stroke, and to equalize the aggregate forces acting on the oppositely reciproostin piston groups at all points of the working cycle. 7

4. A two-stage motor-compressor unit according to claim 1, in which the initial suction pressure 100, the first stage delivery pressure y the second-stage delivery pressure 102, the areas S1 of the first stage compressor piston, S3 of the second-stage compressor piston, and Se of the auxiliary. compensating piston, are so chosen as substantially to satisfy the following relations:

5. A two-stage motor-compressor unit according to claim 1, in which the space between the inactive faces of said low and high-pressure compressor pistons is inclosed in a closed casing and used as a scavenging gas compressor.

- 6. A two-stage motor-compressor unit according to claim 1, in which the low-pressure compressor cylinder is made double-acting and is adapted to compress gas on the return stroke for scavenging purposes.

7. A two-stage motor-compressor unit according toclaim l, in which the'iow-pressure compressor cylinder is made double-acting and is adapted to compress gas on the return stroke for scavenging purposes, and in which the space between the low and high-pressure compressor cylinders is inclosed in a closed casing and used as a scavenging air reservoir. 7

8. A multi-stage internal-combustion free and opposed piston motor-compressor unit comprising in combination a motor cylinder, axially movable motive pistons in said cylinder, a combustion chamber between said motive pistons, a compressor system of lower mean pressure having at least one compressor cylinder and one compressor piston at one end of said motor cylinder, 2. second compressor system of higher mean pressure having at least one compressor cylinder and one compressor piston at the other end of said motor cylinder, rigid operative connections between'said motive pistons and said compressor pistons, re-- spectively, and auxiliary compensating cushion cording to claim .8, in which the pressure in said auxiliary compensating means is substantially constant during the operation of the said compensating piston and equal to the pressure of a higher pressure stage.

10. A two-stage motor compressor unit, according to claim 1,- in which the pressure in said auxiliary compensating cylinder is substantially constant and equal to the delivery pressure of said high pressure stage.

RAUL PATERAS PESCARA. 

